This invention relates to a cathode ray tube and more particularly a structure for preventing reflection at the panel surface of a cathode ray tube.
Generally, the panel surface of the cathode ray tube is flat and smooth and strongly reflects external light, thus making it difficult to view a picture image displayed on the screen. As an approach to this problem, an improved cathode ray tube has been proposed in which the panel surface is subjected to a non-glare treatment so as to diffuse and reflect the external light. Various methods have been proposed for causing diffused reflection at the panel surface. According to one method, glass of the panel surface of the cathode ray tube is selectively etched with hydrofluoric acid for rendering irregular or coarse the panel surface. This method is used practically in certain cases by carefully controlling the conditions of the method, but this method accompanies such various problems that there is a tendency of raising environmental pollution, that tube is liable to be damaged, that the reclaiming is impossible, and that this method can not be applied to finished tube. According to another method, so-called sandblast method, a polishing agent is blasted against the pannel surface to render it irregular. This method is disadvantageous in that it is impossible to obtain uniform quality, that reclaiming is impossible, and that there is a fear of contamination caused by such a foreign matter as polishing agent. According to still another method, a plastic film is coated on the panel surface. But this method is also problematic in that the surface of the plastic film is liable to be damaged or scratched, and that the plastic film is dissolved in an organic solvent.
According to a method disclosed in Japanese Utility Model Publication No. 11150/69, an alkali salt aqueous solution of silicic acid (generally called water glass) is sprayed onto the panel surface of the cathode ray tube with a spray gun or the like and then the sprayed panel surface is heat treated to form an irregular or uneven film on the panel surface. In this method, however, since the applied solution contains alkali, the film reacts with moisture in air to become milky white or the film surface dissolves. Therefore, this method is not practical. Japanese Utility Model Publication No. 26277/75 discloses a method of forming a film having fine irregularity by spraying a mixed solution of silicon tetrachloride and alcohol or ester on the surface of the panel of a cathode ray tube. This method can provide an excellent film. But, the sprayed solution is acidic containing hydrochloric acid, resulting in problems that the spray nozzle is corroded, and that the solution must be stored and handled carefully. Moreover, if reacting on the electron gun, halogen ions of the hydrochloric acid will decrease its emission capability to decrease life of the cathode ray tube. Usually, in the massproduction process, it happens that unsealed cathode ray tubes are laid near a cathode ray tube to be sprayed (this cathode ray tube has been sealed) and residual halogen ions prevailing after completion of spraying tend to react on the unsealed cathode ray tubes. Accordingly, it is necessary to perfectly remove the residual halogen ions with the result that the number of fabrication steps is increased to increase cost of fabrication.